The invention relates to the monitoring of a crystal within a solution to determine whether of not it is growing or dissolving as desired.
Heretofore, the most common noninvasive method used to observe the face of a crystal which is undergoing either growth or dissolution has been to observe the face of the crystal with a measuring microscope. However, this method requires that the microscope monitor be quite close to the crystal and, therefore, only a small portion of the crystal can be examined at a time. The experimenter is usually interested in the crystal as a whole, and this is a considerable disadvantage. The examination of the crystal face in small segmented forms is not a particularly accurate method for determining the state of the crystal as a whole.
Optical systems commonly known as Schlieren systems have been utilized to study density gradients in transparent substances by viewing refractive index gradients. In the Schlieren method, light from a slit is collimated from a lens and focused onto a knife edge by a second lens. The test volume being studied is placed between the two lenses and the deflection pattern that results is viewed on a screen placed behind the knife edge. The deflection is related to the refractive index gradient which is, in turn, related to the density gradient of the test volume. In U.S. Pat. No. 4,391,518 a method is disclosed for utilizing a dual laser optical system for the visualization of phenomena in transparent substances which induce refractive index gradients such as fluid flow and pressure.
While Schlieren techniques are generally well known in the art, their use in monitoring crystal growth has not been heretofore proposed. The prior usages of the well-known Schlieren techniques have not suggested that these techniques would be an expedient to the monitoring of crystal growths.
An important object of the present invention is to provide a technique for monitoring a crystal within a solution to determine whether or not it is growing or dissolving wherein generally the entire face of the crystal may be monitored for accurate testing.
Still another important object of the present invention is to provide a method for monitoring the entire face of a crystal being dissolved or grown in a solution without invading the controlled environment of the solution in which the crystal is being processed.